1. Field of the Invention
This invention relates to circular knitting yarns into fabrics, and specifically to circular knit, elastic fabrics of at least one of single jersey, French terry, and fleece comprising both spun and/or continuous filament hard yarns, and bare elastomeric yarns. In particular, the presently claimed and disclosed invention relates to fabrics that have been circular knitted in a manner in which the draft of the bare elastomeric yarn is controlled so as to provide a finished fabric having predefined use characteristics without the need for an additional heat setting step.
2. Brief Description of the Art
Single knit jersey fabrics are broadly used to make underwear and top-weight garments, such as T-shirts. Compared to woven structures, the knit fabric can more easily deform, or stretch, by compressing or elongating the individual knit stitches (comprised of interconnected loops) that form the knit fabric. This ability to stretch by stitch rearrangement adds to the wearing comfort of garments made from knit fabrics. Even when knit fabrics are constructed of 100% hard yarns, such as cotton, polyester, nylon, acrylics or wool, for example, there is some recovery of the knit stitches to their original dimensions after imposed forces are removed. This recovery by knit stitch rearrangement, however, is generally not complete because the hard yarns, which are not elastomeric, do not provide a recovery force sufficient to completely rearrange the knit stitches. As a consequence, single knit fabrics may experience permanent deformations or ‘bagging’ in certain garment areas where more stretching occurs, such as at the elbows of shirt sleeves, for example.
To improve the recovery performance of circular, single knit fabrics, it is now common to co-knit a small amount of an elastomeric fiber, such as a spandex fiber, with the companion hard yarn.
Traditionally, if heat-setting is not used to “set” the spandex after the fabric is knitted and released from the constraints of the circular knitting machine, the stretched spandex in the fabric will retract to compress the fabric stitches so that the fabric is reduced in dimensions compared to what those dimensions would be if the spandex were not present.
Heat setting is not used for all varieties of weft knit elastic fabrics. In some cases a heavy knit will be desired, such as in double knits/ribs and flat sweater knits. In these cases, some stitch compression by the spandex is acceptable. In other cases, the bare spandex fiber is covered with natural or synthetic fibers in a core-spinning or spindle-covering operation, so that the recovery of the spandex and resultant stitch compression is restrained by the covering. In still other cases, bare or covered spandex is plated only on every second or third knit course, thereby limiting the total recovery forces that compress the knit stitches. In seamless knitting, a process wherein tubular knits are shaped for direct use while being knitted on special machines, the fabric is not heat set because dense, stretchy fabric is intended. For circular knit, elastic single jersey fabrics made for cutting and sewing, however, wherein bare spandex is plated in every course, heat setting is almost always required.
Heat setting has several disadvantages. Heat setting is an extra cost to finish knit elastic fabrics that contain spandex, versus fabrics that are not elastic (rigid fabrics). Moreover, high spandex heat setting temperatures can adversely affect sensitive companion hard yarns, e.g., yellowing of cotton, thereby requiring more aggressive subsequent finishing operations, such as bleaching. Aggressive bleaching can negatively affect fabric tactile properties, for example, the “hand” of the fabric, and usually requires the manufacturer to include fabric softener to counteract bleaching. Furthermore, certain fibers cannot withstand high temperature heat treatment. Heat-sensitive hard yarns, such as those from polyacryonitrile, wool and acetate, cannot be used in high temperatures spandex heat setting steps, because the high heat setting temperatures will adversely affect such heat-sensitive yarns. Finally, other fibers are sensitive to heat due to low fiber melting point. Polypropylene, for example, has a softening point of 155° C., which renders it unsuitable for fabric processing which requires heat setting.
The disadvantages of heat setting have long been recognized, and, as a result, spandex compositions that heat-set at somewhat lower temperatures have been identified (U.S. Pat. Nos. 5,948,875 and 6,472,494, both of which are hereby expressly incorporated herein by reference in their entirety). For example, the spandex defined in U.S. Pat. No. 6,472,494 has a heat set efficiency greater than or equal to 85% at approximately 175° C.-190° C. The heat set efficiency value of 85% is considered a minimum value for effective heat setting. It is measured by laboratory tests comparing the length of stretched spandex before and after heat setting to the before-stretched spandex length. While such lower heat setting spandex compositions provide an improvement, heat setting is still required, and the costs associated with it have not been significantly reduced.
The traditional practice of making and heat setting circular knit fabrics has further disadvantages. The knit fabric emerges from a circular knitting machine in the form of a continuous tube. As the tube is formed in knitting, it is either rolled under tension onto a mandrel, or it is collected as a flat tube under the knitting machine by plaiting, or loose folding. In either case, the fabric establishes two permanent creases where the fabric tube has been folded or flattened. Although the fabric is “opened” by slitting the fabric tube along one of the creases, subsequent use and cutting of the fabric usually mutt avoid the remaining crease. This reduces the fabric yield (or the amount of knit fabric that can be further processed into garments).
In view of the foregoing disadvantages, methods are needed for making circular knit, elastic fabrics of at least one of single jersey, French terry and fleece that have bare elastomeric material plated with spun and/or continuous filament hard yarns, and that avoid the costs and disadvantages associated with the prior art heat setting methods. Additionally, the-invention allows circular knit, elastic fabrics of at least one of single jersey, French terry and fleece to be formed (stabilized, dyed, and finished) as a tube, which has material usage advantages over the prior art.